#include <fstream.h>
#include <math.h>
int main ()
{
ifstream f ("ciur.in");
ofstream g ("ciur.out");
 char a[2000000];
 long n,i,j,l=0;
f>>n;
for (i=1;i<=n;i++) a[i]=0;
for (i=2;i<=sqrt(n);i++)
 if (a[i]==0)
   for (j=i+i;j<=n;j=j+i) a[j]=1;
for (i=2;i<=n;i++) if (a[i]==0) l++;
g<<l<<'\n';
return 0;
}